1. Field of the Invention
The present invention relates to a structure for enhancing torque output of an electric drill, in which a locating gear ring is included in a torque output unit and provided with stop lugs to engage with open recesses provided on an internal gear of the torque output unit and on an inner housing of a torque control unit, so that the torque output unit and the torque control unit are firmly held to each other without the risk of slippage even at a large torque output; and an intermediate washer is positioned between the internal gear and the locating gear ring of the torque output unit to isolate rear parts of the electric drill from any reaction force generated and backward transmitted during operation of the electric drill, making it possible to snap-fit instead of screwing a motor bedplate to the torque control unit and enclose the torque output unit in the torque control unit-at reduced assembling cost.
2. Description of the Prior Art
A conventional electric drill typically includes a torque control unit A1 and a torque output unit A2. Please refer to FIG. 1. The torque control unit A1 includes a torque control member All mounted to a front end of an inner housing A10; and the torque output unit A2 is mounted in the inner housing A10 and includes from front to rear side a main shaft A21, an internal gear A22, a first group of powder metallurgic pinions A23, a transmission gear disc A25, a second group of powder metallurgic pinions A27, a motor bedplate A28, and a motor gear A29 for transmitting power from a motor to the torque output unit. The main shaft A21 has a front end rotatably connected to the torque control unit A1. The first group of powder metallurgic pinions A23 are supported on pins A211 provided at a rear end of the main shaft A21 to locate in and mesh with an internally toothed wall of the internal gear A22. The transmission gear disc A25 includes a front gear portion that forward extends to locate among and mesh with the first group of powder metallurgic pinions A23, and rearward extended pins A251 that support the second group of powder metallurgic pinions A27 thereon. The motor bedplate A28 is then screwed to the rear end of the inner housing A10 with fastening means to enclose the entire torque output unit A2 in the inner housing A10.
To avoid the motor bedplate A28 from direct contact with the second group of powder metallurgic pinions A27 in front of it to cause any damage due to friction, a washer A281 is positioned between the pinions A27 and the motor bedplate A28.
Please refer to FIG. 2. When the electric drill is switched on, power generated by a motor is transmitted via the motor gear A29 to the second group of powder metallurgic pinions A27 that mesh with the motor gear A29, so that the transmission gear disc A25, the first group of powder metallurgic pinions A23, the internal gear A22, and the main shaft A21 work synchronously to output a torsion force.
The conventional electric drill with the above-described torque output structure has the following disadvantages and therefore does not work as well as it is expected:
1. The torque output unit A2 is in the form of an integral assembly that does not effectively prevent transmission of stress and therefore results in considerable damage to internal components of the electric drill due to the stress.
2. With the integral assembly of the torque output unit A2, an overly high reaction force is generated when the electric drill is in use. The high reaction force tends to spring the motor bedplate and necessitates fixing of the motor bedplate to the inner housing with screws. Therefore, increased time and labor costs for assembling the motor bedplate are required.
3. There is not any isolating member between the internal gear and the powder metallurgic pinions, and both the first and the second groups of pinions are located in and mesh with the internal gear to subject to a direct load. It is therefore necessary to produce the internal gear and the pinions through powder metallurgy at increased material cost.
4. The conventional internal gear has large axial size and is produced through powder metallurgy, and therefore requires increased material cost. In the above-described structure, the torsional force output by the torque output unit A2 is transmitted to the torque control unit A1 through engagement of steel balls A101 inside the inner housing A10 with a toothed portion A221 at the front end of the internal gear A22. This type of engagement is able to bear torque output from first to twentieth gear without causing slippage of the steel balls A101 in the toothed portion A221 of the internal gear A22. However, when the torque control unit A1 is adjusted to produce a torsional force higher than the twentieth gear, the steel balls A101 slip in the toothed portion A221 of the internal gear A22 to reduce the performance of the electric drill.
It is therefore desirable to develop a structure for enhancing torque output of electric drill to eliminate drawbacks existing in the conventional electric drill.
A primary object of the present invention is to provide a structure for enhancing torque output of electric drill to solve the problem of damaged components due to backward transmitted reaction force when the electric drill operates. To achieve this object, the structure of the present invention includes a locating gear ring behind the internal gear and an intermediate washer located between the internal gear and the locating gear ring. The intermediate washer effectively isolates power components at rear part of the electric drill from reaction force generated and backward transmitted when the electric drill is operating, and thereby protects the power components against damage due to any stress.
Another object of the present invention is to provide a structure for enhancing torque output of electric drill, in which the internal gear has a reduced axial size due to inclusion of the locating gear ring in the whole structure. That is, the powder metallurgic internal gear may be produced at reduced material cost.
A further object of the present invention is to provide a structure for enhancing torque output of electric drill, in which the intermediate washer isolates the motor bedplate from the reaction force of the electric drill in operating, making it possible to snap-fit the motor bedplate to the inner housing to save material and time for producing and threading screws for fastening the motor bedplate to the inner housing.
A still further object of the present invention is to provide a structure for enhancing torque output of electric drill, in which the intermediate washer isolates the second group of pinions from the reaction force of the electric drill in operating, making it possible to use the locating gear ring and the second group of pinions made of less strong plastic material. The plastic material is less expensive and the cost for injection molding of plastics is lower than the powder metallurgy, enabling the electric drill to be produced at reduced cost.
A still further object of the present invention is to provide a structure for enhancing torque output of electric drill to overcome the problem of slipped internal gear when an overly high torsional force is output. To achieve this object, the internal gear and the inner housing are provided on outer and inner wall surfaces, respectively, with open recesses, and the locating gear ring is provided on its outer wall surface with stop lugs for engaging with the open recesses on the internal gear and the inner housing, such that the internal gear is firmly held to the inner housing without the risk of slippage even at a high torque output.